The present invention concerns a new agent for sizing in the paper industry, more particularly of paper and cartons, consisting of a cationic diurethane dispersed in an aqueous medium in the form of latex, and the process of preparation thereof and of sizing paper therewith.
Cationic urethanes, utilized as sizing agents for the paper industry, are already the object of patents. We are always dealing with cationic polyurethanes or oligourethanes. It is, for instance, known to prepare a quaternary ammonium compound, from a prepolymer with an NCO end group, obtained by the addition of a polyisocyanate to an aliphatic monomer dihydroxylated compound, extended by an aliphatic diol containing a salifiable and/or quaternizable tertiary nitrogen atom. This is the case, for instance, in French Patent No. 2,256,937.
Described in French Patent No. 2,322,236 are cationic polyurethanes that are reaction products of polyisocyanates of the diphenylmethane series containing C.sub.5 -C.sub.12 N-alkyldialkanolamines with a C.sub.1 -C.sub.6 alkyl chain and possibly with reactive groups serving as chain breaker, and polyurethanes carrying protonized and/or quaternized ammonium groups, in solution in water and used for paper sizing. These products, having a low molecular weight and although hydrophilic, are recognized by their inventors as being effective, as compared to the previously known cationic products for paper sizing.